Fuel thermal capacitance for pulsed platform loads

Abstract

A thermal management system for a pulse load on an aircraft. The thermal management system utilizing the reserve fuel from the aircraft to create thermal capacitance such that the instantaneous capacity of the cooling system to remove heat from the aircraft may be sized less than the rate of heat generated by the pulsed load (e.g. laser, radar, rail gun etc.) The reserve fuel is maintained at a temperature in a reservoir and cooled via a cooling system. Fuel from the reservoir is selectively mixed with fuel exiting the pulsed load heat exchanger to provide fuel to the inlet of the heat exchanger at a predetermined temperature, the temperature based at least upon the heat generated by the laser, flow rate of fuel and efficiency of the heat exchanger.

What is claimed is: 
     
       1. A system, comprising:
 a fuel tank; 
 a reservoir; 
 a cooling system; 
 an intermittent heat generating device; the intermittent heat generating device having a peak heat output greater than a peak cooling capacity of the cooling system; 
 a first fuel loop, a second fuel loop and a fuel charging line; 
 the first fuel loop comprising a recirculating path through a first heat exchanger in thermal communication with the cooling system, a first pump and the reservoir; 
 the second fuel loop comprising a second recirculating path through a second pump, a second heat exchanger in thermal communication with the intermittent heat generating device and a variable mixing valve; 
 the variable mixing valve having a first input, a second input and an output, the output to the second fuel loop, the first input from the first fuel loop and the second input from the second fuel loop; a ratio of the second input over the first input being variable; 
 the fuel charging line comprising a fuel path between the reservoir and the fuel tank and a reservoir charge pump in the fuel path; and, 
 the first fuel loop in fuel connection with the second fuel loop via the mixing value and a return line; the return line communicating from a fuel outlet of the intermittent heat generating device to a check valve on the first fuel loop. 
 
     
     
       2. The system of  claim 1  further comprising a vent from the reservoir to the fuel tank. 
     
     
       3. The system of  claim 1 , wherein the second heat exchanger has a fuel inlet temperature and a fuel outlet temperature. 
     
     
       4. The system of  claim 3 , wherein the ratio is a function of a first fuel input temperature. 
     
     
       5. The system of  claim 1 , wherein the fuel inlet temperature is predetermined as at least a function of fuel flow rate through the heat exchanger. 
     
     
       6. The system of  claim 5 , wherein the predetermined inlet fuel temperature is constant for a given fuel flow rate. 
     
     
       7. The system of  claim 5 , wherein the ratio is a function of the predetermined inlet fuel temperature. 
     
     
       8. The system of  claim 1 , further comprising a one-way valve at an interface connecting the return line to the first loop, the one-way valve allowing fuel from the return line into the first loop and preventing fuel from the first loop from entering the return line. 
     
     
       9. The system of  claim 1 , wherein the cooling system via the first heat exchanger removes heat from the first loop. 
     
     
       10. The system of  claim 9 , wherein the cooling system is activated as at least a function of a temperature of fuel in the reservoir. 
     
     
       11. The system of  claim 1 , wherein a fuel capacity of the reservoir is greater than the fuel capacity of the first loop and a fuel capacity of the fuel tank is greater than the fuel capacity of the reservoir, first loop and second loop combined. 
     
     
       12. The system of  claim 11 , wherein the fuel capacity of the reservoir, first loop and second loop are 10 percent or less than the capacity of the fuel tank. 
     
     
       13. The system of  claim 1 , wherein the intermittent heat generator is a directed energy weapon, radar system or electromagnetic rail gun. 
     
     
       14. The system of  claim 1 , where the ratio R is determined according to the following function: 
       
         
           
             
               R 
               = 
               
                 
                   ( 
                   
                     
                       T 
                       inlet 
                     
                     - 
                     
                       T 
                       R 
                     
                   
                   ) 
                 
                 
                   ( 
                   
                     
                       T 
                       o 
                     
                     - 
                     
                       T 
                       inlet 
                     
                   
                   ) 
                 
               
             
           
         
         where T inlet  is a predetermined fuel inlet temperature of the second heat exchanger, T R  is temperature of the fuel in the reservoir and T O  is the fuel outlet temperature of the second heat exchanger. 
       
     
     
       15. A method of cooling an intermittent heat generating device, the method comprising:
 charging a reservoir and fuel circulation lines with fuel from a fuel tank on the mobile platform; 
 maintaining the reservoir at a first temperature; 
 circulating fuel through the fuel circulation lines and the reservoir; 
 predetermining a fixed temperature for fuel entering a heat exchanger as a function of fuel flow rate through the heat exchanger, the heat exchanger in thermal communication with the intermittent heat generating device; 
 mixing, via a variable mixing valve, fuel from the reservoir at the first temperature and fuel exiting the heat exchanger together to output fuel at the predetermined fixed temperature, wherein the ratio of the amount of fuel exiting the heat exchanger that is mixed over the amount of fuel from the reservoir that is mixed is a function of the first temperature, the predetermined fixed temperature and a temperature of the fuel exiting the heat exchanger; 
 supplying the fuel output from the mixing step to the heat exchanger; and, 
 transferring heat from the heat exchanger to the fuel in the heat exchanger. 
 
     
     
       16. The method of  claim 15 , wherein the step of mixing fuel comprising recirculating at least a portion of the fuel exiting the heat exchanger to the variable valve and a remainder of the fuel exiting the heat exchanger to the reservoir. 
     
     
       17. The method of  claim 16 , comprising cooling the remainder of the fuel prior to recirculating to the reservoir; wherein the step of cooling is at a rate less than the instantaneous rate of heat generation by the intermittent heat generating device. 
     
     
       18. The method of  claim 15 , determining the ratio R with the function: 
       
         
           
             
               R 
               = 
               
                 
                   ( 
                   
                     
                       T 
                       inlet 
                     
                     - 
                     
                       T 
                       R 
                     
                   
                   ) 
                 
                 
                   ( 
                   
                     
                       T 
                       o 
                     
                     - 
                     
                       T 
                       inlet 
                     
                   
                   ) 
                 
               
             
           
         
         where T inlet  is a predetermined fuel inlet temperature of the second heat exchanger, T R  is temperature of the fuel in the reservoir and T O  is the fuel outlet temperature of the second heat exchanger. 
       
     
     
       19. The method of  claim 15 , wherein at least a portion of the fuel in the reservoir represents a fuel reserve, the fuel reserve being pumped from the reservoir to the gas tank when the reserve fuel is required. 
     
     
       20. The method of  claim 15 , further comprising the step of supplying a portion of the fuel exiting the heat exchanger to an engine powering the intermittent heat generating device. 
     
     
       21. The method of  claim 15 , further comprising circulating fuel from the fuel tank through the reservoir if the temperature of fuel in the fuel tank is less than the temperature of the reservoir. 
     
     
       22. The method of  claim 15 , further comprising circulating fuel from the reservoir to the fuel tank is the fuel in the fuel tank exceeds a defined temperature.